Increasing evidence suggests that the kidney is the primary site of degradation of extracellular glutathione and the conversion of glutathione conjugates to mercapturic acids. Both pathways required the participation of gramma-glutamyltranspeptidase and of a peptidase activity which is capable of hydrolyzing cysteinyl glycine and its S-derivatized conjugates. We have purified both enzymes following their solubilization from rat renal brush border membranes with either Triton X-100 or treatment with papain. The difference in the physical characteristics of the two forms of the enzymes and their ability to bind to lecithin vesicles suggests that both the gamma-glutamyltranspeptidase and the peptidase are anchored in the brush border membrane through hydrophobic sequences of amino acids. The proposed characterization of these two enzymes should provide information regarding the size and composition of the peptides released by papain. Experiments with isolated rat renal brush border membranes will be carried out in order to investigate the oganization of the two within the membrane and their extent of interaction. Experiments with isolated kidney cells will be carried out to test the participation of these two activities in renal processing of glutathione and of mercapturic acid precursors.